Envelope feeding mechanism



Oct. 23, 1951 A. NOVICK 2,572,509

ENVELOPE FEEDING MECHANISM Filed March 11, 1949 7 Sheets-Sheet l l G) & BY

A T TORNE Y5 IN VEN TOR. Abra/1am Nov/ck Oct. 23, 1951 A. NOVICK 2,572,509

ENVELOPE FEEDING MECHANISM Filed March 11, 1949 7 Sheets-Sheet 2 IN VEN TOR. Abra/mm Nov/ck A T TORNEYS Oct. 23, 1951 A. NOVICK ENVELOPE FEEDING MECHANISM '7 Sheets-Sheet 5 Filed March 11, 1948 IN VEN TOR. Akita/7am Nov/ck A T TORNE Y5 A. NOVICK ENVELOPE FEEDING MECHANISM Oct. 23, 1951 7 Sheets-Sheet 4 Filed March 11, 1949 INVENTOR. Abraham Nov/ck ATTORNEYS;

Oct. 23, 1951 A. NOVlCK ENVELOPE FEEDING MECHANISM '7 Sheets-Sheet 5 Filed March 11, 1949 INVENTOR.

Aha/1am Now'c/r ATTORNEY-5' Oct. 23, 1951 A. NOVICK ENVELOPE FEEDING MECHANISM 7 Sheets-Sheet 6 Filed March 11, 1949 I INVHVTOR. Abra/7am A ow'crr AT TORNE Y3 Oct. 23, 1951 A. NovlcK 2,572,509

ENVELOPE FEEDING MECHANISM Filed March 11, 1949 '1 Sheets-Sheet v fig/l IN VEN TOR. Abra/mm Ivor/ck aw-f/ggj A T TORIVE Patented Oct. 23, 1951 ENVELOPE FEEDING MECHANISM Abraham Novick, Flushing, N. Y., assignor to F. L. Smithe Machine 00., Inc., New York, N. Y., a corporation of New York Application March 11, 1949, Serial No. 80,842

7 Claims. 1

This invention relate to envelope feeding mechanism and more particularly to mechanism which is designed to act upon envelopes whose manufacture is complete except for the printing. It is important in connection with the printing operation that the envelopes be advanced in properly timed and spaced relation. Such timing and spacing can be conveniently obtained by the use of a pin conveyor having pins disposed at uniform intervals which are adapted to engage in the corners between the folded over sealing flaps and the envelope backs.

The primary object of the present invention is to provide simple and practical mechanism for delivering envelopes from stack formation to a conveyor of the kind referred to.

In dealing with this problem it is desirable that an envelope be on hand and ready to be carried away each time that a pair of pins of the pin conveyor arrives at the envelope pick-up station. It is not desirable, however, to crowd the envelopes in dense formation toward such station, for then the withdrawal of one envelope would be apt to disarrange one or more of the following envelopes of the stack, either dislodging or skewing the envelopes, and interfering with the proper and orderly automatic operation of the machine.

In accordance with an important feature of the present invention, a stack conveyor is pro- A vided which is adapted to be driven at either of two predetermined speeds. While envelopes differ in thickness and the frequency of envelope delivery cannot, therefore, be precisely forecast for either of the predetermined conveyor speeds, the conveyor speeds are so chosen that one of them will cause the envelopes to be delivered at a frequency exceeding the supply requirements of the pin conveyor, while the other will cause the envelopes to be delivered at a frequency less than the supply requirements of the pin conveyor. By switching back and forth between the high and low speeds of the two-speed conveyor, the conveyor is caused to deliver the envelopes at an average frequency corresponding precisely with the supply requirements of the pin conveyor. The control is such that the envelopes are caused to approach the transfer point slowly enough to permit the envelopes at the leading end of the stack to spring apart. This reduces the stack density so that each envelope can be readily picked up without disarranging following envelopes.

For reducing the stack density at the point of delivery to the pin conveyor and for enabling the stack density to be automatically measured and used for controlling the two-speed conveyor in the manner just referred to, a light source is disposed alongside the stack to project light upon and between lower corners of the envelopes as they near the pickup point. A photoelectric cell is arranged to be responsive to the light that passes through a corner of the stack. The intensity of the light is affected by the density of the stack through which the light passes, and the density of the stack depends primarily upon the average frequency of envelope delivery. The photoelectric cell output is amplified and acts through a relay to control mechanism for automatically reducing the speed of the two-speed conveyor when the stack density is greater than that desired, and for automatically increasing the speed of the two-speed conveyor when stack density is less than that desired.

The projection of light across a stack corner and the utilization of the transmitted light to control operating mechanism of any kind is believed to be broadly new.

Other objects and advantages will hereinafter appear.

In the drawing forming part of this specification Fig. 1 is a view in side elevation, partly diagrammatic, of an illustrative machine embodying features of the invention;

Fig. 2 is a view in sectional elevation taken upon the line 22 of Fig. 1 in the direction indicated by the arrows, the View being upon a considerably larger scale than Fig. 1;

Fig. 3 is a fragmentary plan view showing the delivery end of the stack conveyor and an associated density meter;

Fig. 4 is a fragmentary view showing a group of envelopes puffed out as they would be at the delivery end of the stack conveyor, the view being taken upon the line 4-4 of Fig. 2 in the direction indicated by the arrows;

Fig. 5 is a fragmentary View showing a group of envelopes in compact formation as they would be throughout most of the length of the stack;

Fig. 6 is a fragmentary vertical sectional view of a portion of the transmission mechanism through which the stack conveyor is driven, the view being taken upon the line 66 of Fig. 7 in the direction indicated by the arrows;

Fig. 7 i a fragmentary, horizontal sectional view taken upon the line 1-? of Fig. 6 in the directions indicated by the arrows;

Fig. 8 is a fragmentary, vertical sectional view 3 taken upon the line 88 of Fig. 6 in the direction indicated by the arrows;

Fig. 9 is a fragmentary, vertical sectional view taken upon the line 9-8 of Fig. 6 in the direction indicated by the arrows;

Fig. is a detail sectional view through a roller clutch which forms part of the transmission train through which the stack conveyor is driven; and

Fig. 11 is an electrical diagram showing the circuits and electrical mechanism through which the stack conveyor drive is controlled;

The illustrative mechanism comprises a printing roller 1 supplied with through transfer rollers 2 and 3 and an impression roller f: The rollers l and E are fast upon shafts 5 and respectively, and these shafts also have fast upon them meshing gears l and 8 whose pitch diameters are equal to the diameters of the-rollers E and 4. The shaft 5' also has fast upon it sprockets 9 which are adaptedto cooperate with conveyor chains it} and I l (Figs. I and 2).

The chain Ii, which isfarther fromthe observer in Fig. 1, runs upon fixedsprockets l2, l3, l4 and I5 which are fast upon shafts i5, ll, [8; and I9; The chains it); which arenearer the observer in Fig. 10, run upon sprockets l-Za, 53a, Ma and I501. which aremounted with capacity for axial adjustment upon the shafts it, l1, l8 and i9, respectively.- The sprocket El nearer the. observer in- Fig. 1 is also correspond ingly adustable axially of the. shaft 6., The chains It and If are provided at uniform intervalswith inwardly reaching fingers. and 21.

The chains. If]. and, II are driven from the shaft is. The shaft I6: is driven from a shaft 22 through a sprocket. 23, a chain 24, and a sprocket 25. The shaft 22 is drivenatconstant speed, and hence the chains. llland l l are caused to travel at a constant speed equalto the circumferential speeds of the rollers. l and, d.

The fingers. 2i. and 2h are designed. to engage at the corners of the leading, envelope of a stack 25 betweenthe back and-the folded down sealing flap of the leading envelope of thestack, and topick the leading envelope away from the stack and carry it forward to the printing instrumentalities. Individual envelopes 27, 28, 29 and 3D areshown in Fig. 1 as'being; carried forward by the pin conveyor.

The envelope stack 26 is shown as supported upon a two-speed conveyor 3| which. carries. the envelopes in stack formation toward the transfer point at which they are picked up by the pin conveyor. Sucker shoes 32' (Figs. 1 and.2) are provided in the path of the envelopes. at the transfer point to free the leading envelope from the stack and keep the envelopes from becoming accidentally disarranged.

The conveyor 3| comprises a pair of chains 33 and 34 which are guided in channel bars 33a and 34a and run upon sprockets 35' and3i car-'- ried by shaft 31 and upon a corresponding pair of sprockets including a sprocket 38 carried by a shaft 39. 34' are fixed on their respective shafts 3! and 39, but the sprockets 35 and 38 which carry the chain 33 are adjustable axially on their shafts to change the spacing of the chains 33 and 34 while maintaining the position of the chain 34 uniform.

The envelopes of the stack 26 are for the most part tightly compressed as shown in Fig. 5. If the stack were initially tightly compressedfrom end to end and the conveyor 31- were advanced The sprockets which carry the chain 4 rapidly enough to cause the blanks to arrive at the transfer point as fast as they are taken away by the pin conveyors, the compressed condition of the stack at the leading 'end thereof would be maintained. If, however, the conveyor 3| is caused to advance the stack so slowly that the envelopes are not delivered as rapidly as they are required by the pin conveyor, the envelopes at the leading end of the stack will tend to spring apart as shown in Fig. 4 as the pressure at the leading end of the stack is relieved. With the envelopes thus separated, they can be conveniently and smoothly picked up by the pin conveyor without frictionally dislodging or disarrang-ing following envelopes of the stack. As soon as this desirable spacing at the forward endof the stacklisachieved, however, the average speed of advance of the conveyor 31 must be increased sumciently to supply the needs of the pin conveyor so that there will not be an accumulating deficiency of blanks at the-transfer point.

In order to achieve an operation of the kind referredto, provision is made for measuringthe density of the stack as it approachestrie transfer point and r for maintaining the average speed of the conveyor at a value to assure that the requirementsof the pin conveyor will besatisfied without any oversupply. By causing the density meter to shift'the stack conveyor drive, speeding up the conveyor 3! when the stack density falls below a desired value andreducingthe' spe'ed of the conveyor 3| when thedensity ofthe stack exceeds a desired value, the desired transfer condition' and the desired average speed may be maintained.

The same shaft 22 which drives the printing mechanism' and thepinconvey'er also drives-the conveyer'3l The drive is transmitted through a V-pulley 46' of fixed diameter and a V-belt 4|; The belt l [also runs upon-a variable diameter V- pulley 42 which is mounted upon and drives-a shaft- 43. The V-belt and V-pulleys constitute elements of a conventional; infinitely variable speeddrivemechanism. Thepulley 42' may, as is well understood, comprise afixed section 44- and a movable section l5 spring urged towardthe section 44.

The pulley and-theshaft 43 are carried upon a frame lfi; which is adjustable-toward and from the shaft 22'. Adjustment of the frame away from theshaft' 22- increases the tension of the belt til and serves-to force the pulley section 45 away from the" fixed pulleysection 44, thereby reducing-the effective diameter of'the pulley 42 and increasing the drive ratio of the belt and pulley' combination. The frame 16 is slidably mounted upon a stationary frame member 41 (Figs. 6 and 9).

The frame 46- comprises upstanding bearing portions 46a and 66b (Figs. 6, '7, Sand 9)*in which certain gears and shafts to be described are mounted, a horizontally disposed base portion 460 and a" downwardly extending vertical web portion 4601. The web portion 46d is maintained in contact with a stationary frame member 41, while a part of the baseportion 46c rides upon the upper face of the stationary frame member 41. The stationary frame member 41 has a rectangular bar 47a secured to it by screws, 41b, whose heads are completely embedded in the bar. The web 4601- of the frame46 is formed with" a channel Me which extends through the web from end't'o end and slidingly receives the stationary bar 41a.

' A headed screw 410 has a comparatively large shank portion 41d disposed within a slot 46f of the web 46d and a reduced shank portion 41c extended through an opening 41 of the frame member 41. The screw 410 is drawn tight to clamp the web 46d against the frame member 41 by a nut 419. A look nut 41b is provided for retaining the nut 419 in clamping position. In order to permit the frame 46 to be shifted, it is necessary that the nuts 41g and 4111. be first loosened. After a new adjustment has been effected, the nuts are again tightened to hold the adjustment.

A threaded rod 48 is screwed into the frame member 46a and is adapted by its rotation to adjust the frame toward and from the shaft 22. The rod 48 is equipped with an operating handle 48. An unthreaded portion of the rod 48 is passed through a bore formed in a bracket member 58, the bracket member being secured upon the stationary frame member 41. Collars 5| pinned to the rod 48 at opposite sides of the bracket 58 prevent the rod from moving longitudinally relatively to the bracket, while permitting it to rotate in the bracket. A set screw 52 threaded through the bracket '58 and having a head 53 which is equipped with arms 54 may be tightened against the rod 48 to lock it in fixed position after an adjustment has been made. This second locking means may be used to supplement the lock provided by screw 41c and nuts 41g and 41h, or in lieu thereof. Either locking means will prevent the frame 46 from shifting accidentally. The purpose of the adjustable speed unit is to enable both speeds of the conveyor 3| to be adjusted relative to the speed of the pin conveyor for different thickness of envelopes.

The shaft 43 is adapted to transmit drive to the conveyor 3| through alternative drive trains. The shaft 43 has fast upon it a worm 55 which drives a worm wheel 56 (Figs. 6, 7 and 9). The worm wheel 56 is supported at one side of a flange 51 formed on a sleeve 58, the sleeve 58 being revolubly mounted upon a shaft 59. Also mounted upon the sleeve 58 at the opposite side of the flange 51 from the worm wheel 56 is a gear 68.

A sleeve 6| is connected to the shaft 59 through a key 62 and held to the shaft by a set screw 63 extends into the space within the worm wheel 56. A disk 64 is mounted upon the sleeve 6| and is secured to the gear 68 by headed screws 65. A ring 66 extends within the worm gear 56 into engagement with the flange 51, and itself includes a circumferential flange 61 which bears against the worm gear 56 in opposition to the flange 51. The screws 65 are passed through disk 64, flange 61, the worm wheel 56, and the flange 51, and are threaded into the gear 68 so that all of these parts travel in unison with one another.

The ring 66 constitutes the outer, driving element of a roller clutch. The sleeve 6| constitutes the inner, driven element of the roller clutch. The sleeve 6| is formed with notches 68 (Fig. in which rollers 69 are received, the rollers being urged outward by compression coil springs 18.

As seen in Fig. 10, the worm wheel 56 is constantly driven in a counter-clockwise direction and transmits drive through the roller clutch to the shaft 59, so long as the shaft 59 is not driven independently of the ball clutch at a greater rotary speed than the rotary speed of the worm wheel 56.

The shaft 59 is connected through a universal joint 1| (Fig. 6) with a sleeve 12 which forms the outer element of a telescoping transmission shaft. The inner element 13 is connected through a key 14 and a slot 15 with the outer element 12. The member 13 is connected through a universal joint 16 (Figs. 1 and 2) with a shaft 11.

The shaft 11, journaled in a frame bracket 18, has fast upon it a worm 19. The worm 19 drives a worm wheel 88 which is made fast with a gear 8|, the worm wheel and a gear combination being revolubly mounted upon a shaft 82 which is supported in the bracket 18. A collar 83 pinned to the shaft 82 maintains the gear BI and the worm wheel 88 in place upon the shaft. The gear 8| drives a gear 84 which is fast upon the drive shaft 31 of the stack conveyor 3| to rotate said shaft in the direction indicated by the arrow in Fig. 2.

The drive train which has been described provides a relatively slow drive of the stack conveyor 3| which is not intended to deliver envelopes rapidly enough to supply the requirements of the pin conveyor.

The alternative drive train goes from the gear 68 to a gear 85 fast upon a shaft 86 (Figs. 7 and 9). The shaft 86 also has fast upon it a gear 81 which drives a long-toothed gear 88. The gear 88 forms one element of a toothed clutch 89. The gear 88 is freely revoluble upon the shaft 59 and is confined between frame member 46b and a shoulder 98 of the shaft 59 and rotates idly while the shaft 59 is being driven by the above described roller clutch.

The toothed clutch face of the gear 88 is adapted to cooperate with a complementary shiftable clutch member 9|. The clutch member 9| is mounted upon the larger portion of the shaft 59 and is connected to it through a key 92 formed on the shaft. The clutch member 9| is formed with a circumferential groove 93 for cooperation with a fork 94 through which the clutch member is controlled and shifted.

The fork member 94 comprises a rock shaft 95 having upwardly extending parallel arms 96 and 91, each arm including at its upper end an inwardly reaching finger or roller 98, which extends into the groove 93. The frame member 46a carries brackets 99 in which bearing pins I88 are mounted and secured by set screws I8I. The bearing pins I88 extend into bores formed in the opposite ends of the rock shaft 95 to support the shaft with capacity for rocking movement. A downwardly extending arm I82 of the rock shaft is connected through a tension spring I83 to an ear |84 of the frame member 461). A set screw I83a serves as a stop for the arm 91 of fork 94 to arrest the latter in its normal position against the action of spring I83. The spring tends to shift the clutch member 9| out of engagement with the clutch face of the gear 88 and thereby to render the second train ineffective to drive the shaft 59.

A laterally extending arm I of the rock shaft is connected through a link I86 with the armature I81 of an electromagnet I88 secured by studs or bolts I88a to the web portion 46d of the frame 46 and which will be described and explained fully at a subsequent point in this specification. When the armature I81 is drawn downward, the rock shaft 95 is rocked clockwise as viewed in Fig. 6 to carry the clutch member 9| into engagement with the clutch face of the gear 88. When this occurs, the second train is made effective to drive the shaft 59 at a considerably higher speed than that at which it is driven through the slip clutch train. The roller clutch (Fig. 10) permits the shaft 59 with its sleeve 6| to rotate faster than the worm wheel 56.

In the illustrative structure, the multiplying train, comprising. gears 51], 85, 81 and 88, drives the shaft at approximately three times the speed at which the shaft is driven from the worm wheel 56' through the slip clutch. Whenever the toothed clutch member 9I is engaged to make the second train effective, therefore, the shaft 59 simply turns faster than, or in other words overruns the worm 553, so that the slip clutch train becomes ineffective. As soon as the clutch member QI is disengaged, however, the fast train is rendered ineffective and the slip clutch immediately and automatically resumes the driving of the shaft 59.

From what has been said it will be apparent that in the illustrative mechanism the conveyor SI is always driven, but that it is driven at two speeds one of which is three times as great as the other, By controlling the time apportioned to the two drive trains the average speed of the conveyor 3i can-be made to have any value between the higher speed and the lower speed. In order that the average speed shall exactly meet the requirements of the pin conveyor, the drive mechanism is controlled from the stack itself,- and in such manner that the envelopes will be uncompressed as they near the transfer point.

For regulatingthe average rate of envelope feed and controlling the stack density, a density meter is provided. The density meter comprises alight its (Figs. 2; 3 and if) and a reflector Ht": disposed to project light downward across a cor her of the stack near the transfer point. A portion of: the light, whose intensity depends upon the density of the envelopes upon the conveyor 3i passes through a slot III in the casing N2 of a photoelectric cell I 9'3 The light is reflected by a reflectingsurface Ht upon the cathode I I5 of the photoelectric cell. This causes a feeble electric current to be generated whosepotential is a function of the intensity of the light which falls upon the cathode 5 iii. The output of the photoelectric cell is utilized for controlling the operation of the electromagnet Hit.

The photoelectric cell H3 and the amplifier tube I It receive their plate voltages from bleeder resistor Md. The bleeder resistor is supplied through: conductors i I'i and H8. The photoelectric cell is: connected to supplygrid voltage to the amplifier. tube HG. One lead I253 runs from the photoelectric cell to the grid of the tube H6, while the other lead I2! is adjustably connected to the resistor I IS. The resistor H9 is connected to the cathode of the tube II 5 through a conduct'or' I22. The conductors I28 and I22 are connected to one another through a resistor 23.

The plate circuit of the tube I ifi'in'cludes a conductor 525 which is connected to the conductor I I8 through a fixed resistor I25. The conductor IE4 is connected through a resistor I25 to the grid of a thyratron I22. The conductor H8 is connected to the cathode of the thyratron I21 through conductors I28 and I29. When the bias of the thyratron grid as controlled from the photoelectric cell attains a predetermined value, the thyratron is tripped and will thereafter pass current from its'cathode to its plate so long as a potential tending to cause current to' flow in that direction is uninterruptedly' maintained, even though the grid bias should subsequently fall below' the value which was required to trip the thyratron in the first place;

Conductors I363 and I31 supplied from a commercial source of alternating current are connected to the primary I32 of a: transformer I 33'.

The secondary I34 of the transformer I33 has one of its ends connected through a conductor I35 with the conductor I29 which runs to the cathode of the thyratron I21. The plate of the thyratron is connected through a conductor I36 with a D. C. relay coil I37, and the circuit is completed from the relay coil I3? to the secondary Iti through a conductor I38.

The tendency of the transformer I33 .is to cause alternating current to flow in the thyratron circuit. Since the thyratron will pass current in only one direction, however, alternate half cycles are passed, while the other alternate half cycles are suppressed. The current that flows through the relay coil i3! is, therefore, direct but intermittent current. The relay armature consists of a switch member I39,- and this is made slow acting enough to remain in its closed position dur ing the half cycles in which the relay coil is unenergized. Because of the fact, however, that during alternate half cycles the. flow of current in the thyratron circuit is interrupted, it is necessary for maintaining the switch 539 in a closed condition that the thyratron grid shall trip off the thyraton at the beginning of each active half cycle. Thus at any time when the thyratron grid bias falls below a predetermined tripping value, the positive half cycles as well as the negative half cycles will be suppressed by the thyratron, and the switch I39 will be permitted to open; The switch I3?) is designed to control the electromagnet I58 which is of the alternating current type. The circuit of electromagnet H38 may be traced out from the conductor I33 through a conductor I 36, switch I39, conductor Mil, electromagnet 588 and conductor Hi2, back to the conductor I 3I.

It will now be apparent that the clutch member 9! is controlled from the photoelectric cell, and that the effect of the photoelectric cell is determined by the stack density. When stack density exceeds a predetermined value, the light transmitted to the cathode I lb of the photoelectric cell is of low intensity, the resulting bias transmitted to the thyratron grid is low,- the thyratron circuit is not tripped, and the switch 539 remains open so that the electromagnet I08 is not energized. The-spring I63 accordingly acts to inaintainthe clutch member 95 out of engagement with the clutch face of the gear 88, so that the lowspeed drive of the conveyor 3I is maintained effective and the high speed drive is maintained ineffective.

I Since the low speed drive is not capable of meeting the requirements of the pin conveyor, the density of the stack near the transfer point will after a time be diminished and more light will be transmitted to the cathode II5 of the photoelectric cell. At a; desired stack density value, the intensity of this light will be sufficient to cause the thyratron to be tripped. The high speed drive for the stack conveyor 3% will thereupon be made effective, and this if maintained long enough would fully recompress the envelopes, As soonas thestack density is increased fromabove the desired critical density, however, the intensity of the transmitted light is again reduced to the point where the thyratron can no longer be tripped; It is evident, therefore, that the: described mechanism will control the stack feed so as to maintain the average rate of envelope delivery exactly equal-'to-the requirements ofthe" pin conveyor and the stackdensity ad- J'acent'the'transfer point ata desired value which enables-the envelopes-to be detached one by'o'ne from the stack without dislodging or disarranging adjacent envelopes of the stack.

I have described what I believe to be the best embodiments of my invention. I do not wish, however, to be confined to the embodiments shown, but what I desire to cover by Letters Patent is set forth in the appended claims.

I claim:

1. In an envelope printing mechanism, the combination with a conveyor having a substantially vertical pick-up stretch and having pins at uniformly spaced intervals for engaging in the corners between the folded-over sealing flaps and the envelope backs to lift the envelopes out of stack formation and positively carry them away in properly timed, individualized relation, of a stack feeder for advancing the blanks in stack formation to the pick-up point of the pin conveyor comprising a stack conveyor along which the stacked envelopes are advanced in upright attitudes, an abutment in the stack path at the pick-up point against which the sealing flap of the leading envelope bears lightly, a density meter for measuring the stack density of the envelopes along a lower corner of the stack near the pick-up point, and mechanism responsive to the density meter to reduce the speed of the stack conveyor below a critical speed when a desired critical density is exceeded and to increase the speed of the stack conveyor to a predetermined, comparatively high speed above the critical speed when the critical density is not maintained.

2. In an envelope printing mechanism having a conveyor which includes a substantially vertical pick-up stretch and which is provided with pick-up pins at uniformly spaced intervals for engaging and pushing the envelopes to advance them positively in properly timed and spaced relation, a stack feeder for advancing the b anks in stack formation to the conveyor comprising a two-speed conveyor along which the stacked envelopes are advanced in upright attitudes toward the pick-up point, a light source disposed to project light between the lower corners of envelopes advanced by the two-speed conveyor as they near the pick-up point, a photoelectric cell responsive to the transmitted light, and mechanism responsive to the photoelectric cell for reducing the speed of the two-speed conveyor when a desired critical envelope density is exceeded and for increasing the speed of the two-speed conveyor when the critical density is not maintained.

3. In an envelope printing mechanism having a conveyor which includes a substantially vertical pick-up stretch and which is provided with pins at uniformly spaced intervals for en aging the corners between the folded-over sealing flaps and the envelope backs to advance the envelopes positively in properly timed and spaced relation, a stack feeder for advancing the blanks in stack formation to the conveyor comprising a twospeed conveyor along which the stacked envelopes are advanced in upright attitudes toward the pick-up point, a light source disposed to project light between the lower corners of enve lopes advanced by the two-speed conveyor as they near the pick-up point, a photoelectric cell responsive to the transmitted light, electrical mechanism responsive to the photoelectric cell comprising an amplifier for the photoelectric cell output, a relay controlled by the amplified output and power mechanism controlled by the re lay to reduce the speed of the two-speed conveyor when a desired critical envelope density 10 is exceeded, and to increase the speed of the two-speed conveyor when the critical density is not maintained.

4. A stack feeder for envelopes comprising, in combination, a stack conveyor for supporting envelopes on edge and advancing them in upright attitudes toward a pick-up point from which they are removed at a constant rate, mechanism for driving the conveyor continually at either one or the other of two predetermined speeds, the one too slow to maintain a critical density and the other too fast to maintain the critical density, and control mechanism for causing the two speed conveyor to deliver the envelopes to the pick-up point in a formation of predetermined density comprising a density meter for measuring the stack density of the envelopes near the pick-up point, and mechanism responsive to the density meter for causing the two-speed conveyor to be driven at the lower of said speeds when a desired critical density is exceeded, and for increasing the speed of the two-speed conveyor to the higher of said speeds when the critical density is not maintained.

5. In an envelope printing machine having an individualizin conveyor for advancing envelopes in predetermined, timed and spaced relation, in combination, mechanism for advancing blanks in stack formation toward a pick-up point at which they are picked up by the individualizing conveyor, comprising a feedin conveyor for advancing the envelopes in stack formation and delivering them at proper average frequency and density to meet the requirements of the individualizing conveyor, mechanism for measuring the density of the envelopes as they near the pick-up point, means for driving the feeding conveyor evenly at a predetermined speed less than that required to maintain the desired frequency of delivery, means for driving the feeding conveyor evenly at a predetermined speed greater than that required to maintain the desired envelope density, and mechanism responsive to said measuring mechanism to increase or diminish the speed of the stack conveyor as required to maintain the desired envelope density and an average rate of delivery equal to the requirements of the individualizing conveyor.

6. An envelope machine comprising, in combination, a conveyor having an upwardly traveling pick-up portion and having pins at uniformly spaced intervals for engaging in the corners between the folded over sealing flaps and the envelope backs to advance the envelopes positively in properly timed and spaced relation, mechanism for driving said conveyor at constant speed, a stack feeder for advancing the blanks in stack formation to the pick-up point of the pin conveyor comprising a two-speed conveyor along which the stacked envelopes are advanced in upright attitudes, a first constantly running transmission train including a slip clutch adapted to drive the two-speed conveyor at a speed lower than that required to produce the required average rate of envelope delivery and a desired, critical envelope density, a second transmission train adapted to drive the two speed conveyor at a speed higher than that required to produce the required average rate of envelope delivery and the desired critical envelope density, a clutch controlling the second transmission train, a light meter for measurin the envelope density of the stack as it approaches the pick-up point, and mechanism responsive to said light meter for controlling the last mentioned clutch.

15A sstrmture as ;-set forth in maim which fiurther innlndes flan i fini y a justable variable UNITED STATES PATENTS speed drive through which both the transmission e :tmins are {driven from the mechanism which 51 4321 R gj A 3 5 .dlEWBS the pin conveyor. f s

ABRAHAM NOVICK i 7 u llksen Aug.,29, 1939 2361,90? Baker etal Nov. 7,1944 REFERENCES CITED 2,449,690 C apman Sept- 2L 1 4 f-Ihe fpllowing references are of record in ;the 

